Instead, Dion thanked his colleagues, the Liberal Party leadership and most of all, his constituents.

"With all my heart, I thank the voters of Saint-Laurent–Cartierville who, a full eight times, placed their confidence in me and gave me the honour of representing them in the House of Commons," he wrote.

He called his two decades in politics "an incredible adventure," saying that while he's leaving active politics, "politics is not the only way to serve one's country."

21 years of service

Dion first entered politics in 1996, as he writes in his statement, at the request of Prime Minister Jean Chrétien.

He served as minister of intergovernmental affairs under Chrétien. It was during this tenure that Dion worked on the Clarity Act, passed in 2000.

The Act established the conditions under which the federal government would approach provincial secession by referendum with a clearly framed question and majority vote.

Dion served as environment minister under Paul Martin from 2004-05. Following the Liberal defeat in 2006, Dion was elected leader of the Liberal Party and leader of the Official Opposition in the House of Commons.

During the 2008 election, the Liberals captured only 26.2 per cent of the popular vote. Dion took responsibility for the loss, saying, "If people are asking why, it's because I failed."

He resigned as leader soon after.

Dion stayed on as an MP until the Liberal Party, led by Justin Trudeau, won in 2015. He was then appointed minister of foreign affairs.

'Today is a day to say thank you'

Saint-Laurent Borough Mayor Alan DeSousa told CBC that he worked closely in collaboration with Dion and that he was "well-liked" in the community.

"People will remember a man who was pleasant, approachable, present in the community," said DeSousa.

"Today is a day to say thank you for all he did."

Saint-Laurent resident Ianthi Greeves told CBC she felt Dion represented the riding with "integrity," and that he proved himself to be "fair and just."

"You know everything must come to an end, I wish him the best of luck."

Dion 'still has a lot to give'

CBC Montreal political analyst and former provincial immigration minister under Jean Charest, Yolande James, said she knew Dion through Liberal Party events.

CBC political analyst and former Liberal MNA Yolande James says Dion may go on to teaching or take a diplomatic post. (CBC)

She says Dion will be remembered as a resilient politician who stayed close to his riding.

"I was always impressed with his capacity to stay in touch and in contact with a lot of people from the different communities. There was no event that was too small, no person that was not as important for him to talk to," said James.

When it comes to his legacy, she says he likely won't disappear from the public eye entirely.

"I don't think Stéphane Dion is someone who is going to disappear from the public sphere altogether, be it in a teaching capacity or a diplomatic post, I think this is somebody who clearly still has a lot to give."